回复：红色单位正方形问题解答

Please clarify. I assume you meant (a), but can be (b) or (c). thanks.


(a) Is it possible to color red some of the unit squares of a 2009x2009 grid
so that every non-red unit square shares a side with exactly one red square,
without two red unit squares share any sides?


(b) Is it possible to color red some of the unit squares of a 2009x2009 grid
so that every unit square, even the red ones, shares a side with exactly one red square,


(c) Is it possible to color red some of the unit squares of a 2009x2009 grid
so that every non-red unit square shares a side with exactly one red square,
but two red unit squares can share any sides?

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• 回复：回复：红色单位正方形问题解答 -群众丁- ♂ (40 bytes) () 05/03/2009 postreply 16:16:02